Lockout/Tagout (LOTO) — Safe Isolation of Machinery and Energy Sources (2026)

Why LOTO Matters

The dangerous moment in machinery work is almost never the running machine — it is the machine that everyone assumes is off. Maintenance, setting, cleaning and clearing blockages all put people inside the danger zone of equipment that, if it started or moved, would cause a crushing, entanglement, amputation or burn injury. The Health and Safety Executive's investigations into machinery fatalities return to the same failures again and again: the machine was not properly isolated, isolation was not locked off, or stored energy was never released.

LOTO removes the assumption. Instead of trusting that a switch is off, you physically isolate every hazardous energy source, lock that isolation so no one can restore it, tag it so everyone knows why, release or restrain any stored energy, and then prove the equipment is at zero energy before anyone touches a moving part. It is a discipline, not a gadget — and it is the difference between a safe job and a fatality.

The Legal Basis

LOTO is not an optional best practice in the UK — it sits on top of clear legal duties. The overarching duty comes from the Health and Safety at Work etc. Act 1974 (HSWA), which requires employers to ensure, so far as is reasonably practicable, the health and safety of workers and others affected by their work. Two more specific sets of regulations turn that general duty into concrete requirements for machinery.

• PUWER 1998 — the Provision and Use of Work Equipment Regulations. PUWER requires that work equipment can be isolated from all its sources of energy, and that maintenance is carried out safely, which in practice means equipment is shut down and de-energised before it is worked on. The principle running through PUWER is "safe isolation": separating the equipment from its energy supply and keeping it separated for the duration of the work.
• Electricity at Work Regulations 1989 — these govern electrical isolation specifically. They require that conductors are isolated and made dead before work, that isolation is secured against reconnection, and that there is no danger of the equipment becoming live again while work is in progress. This is where "proving dead" with an approved voltage tester comes from.

Together these give you the legal foundation for LOTO: PUWER for the machine and all its energy sources, the Electricity at Work Regulations for the electrical case, and the HSWA underpinning the lot. The shared principle is safe isolation — and a lock that physically prevents re-energisation is the strongest form of it.

LOTO Is Not Just Electrical — Isolate Every Energy Source

The single most common and most dangerous misconception is that LOTO means "turn off the power." Electrical energy is only one of the hazards. A machine can be completely dead electrically and still maim someone through stored pressure, a raised load, a wound spring or residual heat. Before you isolate anything, identify every hazardous energy source on the equipment you are working on.

• Electrical: mains supply, control circuits, secondary supplies, on-board batteries and backup power. Isolate at the isolator, lock off, and prove dead.
• Mechanical: moving parts that can move under their own weight or momentum — flywheels, rollers, gravity-fed components, anything that can free-wheel or fall.
• Hydraulic: pressurised fluid in rams, accumulators and lines. Pressure can hold a load up or drive a movement long after the pump stops.
• Pneumatic: stored compressed air in receivers, cylinders and lines. Air pressure does not vanish when the compressor is switched off.
• Stored mechanical: springs under tension or compression, raised platforms, suspended loads, counterweights and any part held up against gravity.
• Thermal: hot surfaces, steam, hot fluids and components that retain heat after shutdown.
• Chemical / process fluids: trapped or pressurised process media — gases, steam, corrosive or flammable liquids in pipework and vessels.

For each source, the job is the same: isolate it, then release or restrain the stored energy. Bleed off hydraulic and pneumatic pressure to atmosphere. Lower or physically block raised parts, rams and platforms. Capture or restrain springs and suspended loads. Discharge capacitors and allow inverters and drives to bleed down. Allow hot components to cool, or work through the thermal hazard with the right controls. A machine is only safe when every one of its energy sources is isolated and its stored energy has been dealt with.

The LOTO Steps

A reliable LOTO procedure follows the same logical sequence every time. The exact detail will be written into the equipment-specific isolation procedure, but the pattern is consistent across machinery and plant.

1. Prepare and identify all energy sources. Before touching anything, work out every hazardous energy source on the equipment — electrical, mechanical, hydraulic, pneumatic, stored mechanical, thermal and process. Notify everyone affected that the equipment is going out of service.
2. Shut down the equipment properly. Bring the machine to a controlled, normal stop using its own controls. Never use an emergency stop as a substitute for isolation — an e-stop holds the machine, it does not isolate it.
3. Isolate each energy source. Operate the isolating device for every source at its isolation point — open the electrical isolator, close the supply valves, disconnect the air and hydraulic lines as required.
4. Lock out. Apply a lockout device and padlock to each isolator so it physically cannot be moved back to the energised position. This is the core control: an isolator that cannot be re-operated cannot re-energise the machine.
5. Tag out. Attach a warning tag at each isolation point stating who applied the lock, why, and when. The tag carries the information; the lock carries the control.
6. Release or secure stored energy. Bleed pressure to zero, lower or block raised parts, discharge capacitors, restrain springs and suspended loads, and allow hot parts to cool. Do not skip this step because the machine is "off."
7. Verify zero energy. Confirm the equipment is genuinely de-energised before any work begins. Carry out a try-to-start test (attempt to operate the machine from its controls — it must not run or move) and, for electrical work, prove dead with an approved voltage tester, proving the tester on a known live source before and after. Only when zero energy is confirmed does the work begin.

Personal Locks and Keys

The power of LOTO comes from one simple rule: each worker applies their own lock and keeps the only key. Nobody else has a key to your lock. While your lock is on, the equipment cannot be re-energised without removing it, and only you can remove it. This guarantees that no one can restore power while you are still inside the machine, because no one else can take your lock off.

Where several people work on the same equipment, a group lock box is used. The isolation is locked off, the keys to those isolation locks go into the lock box, and then every worker applies their own personal padlock to the box. The box cannot be opened — and therefore the keys cannot be retrieved to re-energise the machine — until every individual lock has been removed. The work is only complete when the last person removes their own lock.

The golden rule is that only the person who applied a lock removes it. Removing someone else's lock is one of the most serious breaches in any LOTO system, because it defeats the entire point of personal control. If a lock has to be removed in someone's absence, that requires a formal, managed and documented procedure to account for the person before any energy is restored — never a casual cut of the padlock.

A word on tags: a tag is a warning, not a physical control. A tag tells people the equipment is isolated and should not be operated, but it does nothing to physically stop someone re-energising it. A tag on its own is a weaker control than a lock. Wherever it is reasonably practicable to lock off, lock off — and use the tag to add the information. Tag-only isolation should be the exception, used where a positive lock genuinely cannot be applied, and then only with additional controls.

Permits, Competence and Reinstating Safely

For higher-risk isolations — complex plant, multiple energy sources, multiple trades, or work that interacts with other operations — a permit to work formalises the control. The permit records the isolations made, the precautions taken, who has authorised the work, the scope and duration, and the steps required to hand back. It forces a structured conversation before work starts and a structured sign-off before energy is restored.

LOTO is only ever carried out by competent, trained and authorised people. Isolation, locking off, releasing stored energy and proving dead all require knowledge of the specific equipment and its energy sources. Workers must be trained in the procedure, authorised to apply isolations, and clear on the limits of their authorisation.

Reinstating the equipment is part of the job and is just as disciplined as the isolation. The sequence is: confirm the work is complete and the equipment is fit to run; remove all tools, materials and debris; replace every guard and safety device; check the area is clear and account for everyone who was working on the machine; ensure all personal locks and tags are removed by the people who applied them; warn those nearby; and only then operate the isolators to re-energise and return the equipment to service. Re-energising while someone is still working, or with a guard left off, undoes every precaution that came before it.

The Electrical Case: Safe Isolation

Electrical isolation is the most familiar LOTO scenario and has its own well-established discipline under the Electricity at Work Regulations 1989. The principle is the same as the wider LOTO process — isolate, lock off, prove dead — but the electrical-specific steps of locking off the correct point of isolation, proving dead with an approved voltage tester, and proving the tester on a known source before and after are worth treating in detail.

If electrical isolation is the part of this that applies most to your work, read our dedicated guidance on electrical safe isolation as the electrical-specific case of the broader LOTO principles set out here. The wider lesson holds regardless: electrical isolation alone does not make a machine safe if hydraulic pressure, a raised load or a wound spring is still waiting to release.

Quick Reference: The LOTO Steps

Getting LOTO Right on Every Job

LOTO is not bureaucracy for its own sake — it is the practical reason maintenance engineers, fabricators, facilities teams and mechanical and process trades go home at the end of the day. Build it into the way you work: write equipment-specific isolation procedures, keep a stock of personal padlocks, lockout devices and group lock boxes, train and authorise your people properly, and never let "it'll only take a second" talk you out of isolating. Identify every source, shut down, isolate, lock and tag, release the stored energy, and prove zero energy before you put a hand inside. Every machine, every time.